<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        function add() {
            var num = 0;
            while (num < 5) {
                num++;//num+=1;
            }
            return parseInt(num);
        }
        function showNum() {
            document.write(add());
        }
        showNum();
    </script>
</body>

</html>